1. Field of the Invention
This invention relates to image signal processing. More particularly, this invention relates to image signal processing of image data generated or captured in a frame format and then converted to an interlaced format prior to receipt by a signal processing apparatus.
2. Description of the Prior Art
It is known to provide image signal processing systems, such as digital video effects systems, for manipulating video images. Such systems are well developed and can provide a large range of sophisticated effects. It has been proposed to adapt these video systems so that they are also able to operate with film images. This would enable integration of film and high definition video images and so provide access to the sophisticated effects of the video image systems for film images without having to employ new hardware.
An obstacle to such integration of film and video is that film images are typically captured in a full frame format, whilst video images are captured in an interlaced format. The existing image processing hardware has been developed to handle interlaced format video data father than full frame format data. To overcome this it is possible to convert the full frame format data to interlaced format prior to passing it to the existing image processing hardware. It will be appreciated that the data rate of 60 Hz 2:1 interlaced format data and 30 Hz 1:1 full frame format data are the same for a given array of pixels. Accordingly, this format conversion appears to provide a simple and effective way of integrating video and film.
However, there is a problem with this simple approach. For a fixed data sample rate, full frame format provides greater vertical spatial resolution at the cost of less temporal resolution, whereas interlaced format provides greater temporal resolution at the cost of less vertical spatial resolution. If one simply transforms image data captured in full frame format to interlaced format you don't gain the improved temporal resolution and yet you lose potential spatial resolution through not being supplied with a sequence of adjacent full frame raster lines. As a consequence, any signal processing apparatus using successive lines of image data (e.g. a vertical finite impulse response filter) is only supplied with every other line when using the interlaced format data resulting in a loss of spatial resolution in the signal processing being carried out. An object of the invention is to allow for the integration of full frame and raster image data processing without losing spatial resolution.